1. Field of the Invention
The invention in general relates to remote, acoustically controlled systems and particularly to a receiver for such systems.
2. Description of the Prior Art
The need often arises for the remote control of underwater systems wherein command signals are transmitted acoustically through the water environment, as opposed to a hard wire transmission link. Many systems utilize multi-tone sequential code signaling techniques wherein different combinations of coded groups represent different commands to be carried out by the system. The receiver portion of the system includes a decoder which decodes the different combinations of input codes and provides an appropriate binary coded output for the various control functions.
With a hard wire link, the arrangement works with few, if any, false alarms. However, when the command link is accomplished acoustically through the water, problems arise with respect to, for example, sea state noise interference, multi-path interference, and various engine and mechanical noises present, thus causing a relatively high and objectionable false alarm rate.
To eliminate triggering on false signals, circuits have been constructed incorporating filter banks and threshold logic whereby only certain signals in a particular frequency range and with an amplitude above a certain preset threshold will be utilized in the decoding process. With such an arrangement the false alarm rate is reduced slightly, however various random noises, if above the threshold level, are interpreted as command signals.
Another arrangement which provides highly satisfactory operation utilizes a sophisticated computer for analyzing the incoming signal and supplying the appropriate command signals to the system under control. For many underwater systems, however, size and space requirements are restricted and computer interface requirements are severe.
The receiver of the present invention is a relatively low cost, small sized receiver which will provide the necessary control signals to the remote system with a very low rate of false alarms.